AANEM MONOGRAPH

ULTRASOUND-GUIDED TREATMENT OF PERIPHERAL ENTRAPMENT MONONEUROPATHIES JOHN W. NORBURY, MD,1 and LEVON N. NAZARIAN, MD2 1 Department of Physical Medicine and Rehabilitation, The Brody School of Medicine at East Carolina University, 600 Moye Boulevard, Greenville North Carolina 27834, USA 2 Department of Radiology, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, Pennsylvania, USA Accepted 13 May 2019

ABSTRACT: The advent of high-resolution neuromuscular ultrasound high-resolution linear-array transducers has allowed neu- (US) has provided a useful tool for conservative treatment of periph- romuscular US to emerge as a powerful tool for the diag- eral entrapment mononeuropathies. US-guided interventions require 2–6 careful coordination of transducer and needle movement along with a nosis of peripheral entrapment mononeuropathies. detailed understanding of sonoanatomy. Preprocedural planning and US-guided treatment of entrapment mononeuropathies positioning can be helpful in performing these interventions. Cortico- has also greatly expanded in recent years. Technical steroid injections, aspiration of ganglia, hydrodissection, and minimally invasive procedures can be useful nonsurgical treatments for aspects of performing therapeutic US-guided proce- mononeuropathies refractory to conservative care. Technical aspects dures and the current state of the science regarding US- as well as the current understanding of the indications and efficacy of guided treatment for common peripheral entrapment these procedures for common entrapment mononeuropathies are reviewed in this study. mononeuropathies are reviewed and discussed in this Muscle 60: 222–231, 2019 monograph.

The expansion of high-resolution linear-array trans- TYPES OF ULTRASOUND-GUIDED INTERVENTIONS ducers has allowed neuromuscular ultrasound (US) Injections. suppress 7–9 to emerge as a powerful tool for the diagnosis and treat- proinflammatory cytokines. They are thought to exert ment of entrapment mononeuropathies. In general, a therapeutic effect in entrapment neuropathies by 10,11 these mononeuropathies can be caused by compression suppressing the associated inflammation and edema. at fibro-osseous tunnels, mass effect from adjacent gang- Althoughtraditionallyitwasthoughtthatsteroidsactvia lia, and sometimes biomechanical abnormalities, such as an effect on inflammation in the nerve itself, recent hypermobility or traction. Diagnosis can be made on clini- research suggests that vascular congestion plays a role cal grounds and confirmed by electrodiagnostic (EDx) and this may be decreased by corticosteroids, thereby 11 testing or neuromuscular US. Treatment options for alleviating symptoms. In addition to anti-inflammatory peripheral mononeuropathies include surgery; conserva- effects, a direct analgesic impact may also contribute to 12 tive measures such as education, splinting, nerve glide potency of corticosteroids. In the authors’ experience, exercises, and avoidance of provocative activities; as well the associated with entrapment neuropathies often as injection therapy. Until recently, these injections were has a better response to steroid injections than the performed without image guidance. Although blind neurologic symptoms such as numbness and especially injections for mononeuropathies are often efficacious,1 weakness. Absolute contraindications to corticosteroid they run the risk of either inadvertent nerve damage or injections include allergy to , active infection placement of the injectate in a location that may be too or wound in the area being injected, and severe hyper- far away to have maximum effect. The development of glycemia. Blood glucose levels can remain elevated for 5 days after a local corticosteroid injection, and a hemo- globin A1C greater than 7% is predictive of a higher and Additional supporting information may be found in the online version of 13 this article. longer lasting elevation in blood glucose levels.

Abbreviations: CSA, cross-sectional area; EDx, electrodiagnostic; fl EMG, ; FCR, exor carpi radialis; LCNT, lateral cuta- Hydrodissection, Aspiration of Ganglia, Phenol, or neous nerve of the ; NCS, nerve conduction study; PIN, posterior interosseous nerve; UNE, at the elbow; US, ultrasound Alcohol Blocks, and Minimally Invasive Procedures. Key words: aspiration; corticosteroid injection; entrapment mononeuropathy; Recently, hydrodissection has been explored as an perineural injection; treatment; ultrasound guidance Available for Category 1 CME credit through the AANEM at www.aanem. adjunct to standard corticosteroid injections. In this pro- org. This paper underwent peer review by the AANEM Monograph Review cedure, a large (15 ml or less) volume of anesthetic, and Development/Issues & Opinions Committee and review by the Mus- fl cle & Nerve editor, but did not undergo additional peer review via the saline, or dextrose-containing uidisinjectedinthe Muscle & Nerve editorial process. perineural region in hopes of breaking adhesions that Conflicts of interest: None of the authors have any conflicts of interest to disclose. may be contributing to the mononeuropathy. Hydrodis- section (or hydroneurolysis) has been shown to reduce Correspondence to: J. W. Norbury; e-mail: [email protected] gliding resistance in the carpal tunnel in cadaver © 2019 Wiley Periodicals, Inc. 14 Published online 15 May 2019 in Wiley Online Library (wileyonlinelibrary. models. This technique may be especially helpful in com). DOI 10.1002/mus.26517 situations where scar tissue contributes to the pathology,

222 AANEM Monograph MUSCLE & NERVE September 2019 such as in recurrent (CTS) Either a large-gauge needle17 or a modified surgical after a surgical release.15 An example of fluid dis- instrument18,19 can be used to actually release the nerve section of the from the transverse carpal by mechanically disrupting the structure causing the ligament and subsynovium is shown in the video (refer entrapment, such as the transverse carpal ligament. to Supplementary Material available online). Although these procedures are still relatively uncom- When a mass lesion such as a ganglion is present, mon, they may become an alternative to traditional sur- US-guided needle aspiration is a potential treatment. gical releases. Ganglia appear as cystic masses, often in association with joints or tendon sheaths, although they can also TECHNICAL ASPECTS OF ULTRASOUND-GUIDED be intraneural. They do not demonstrate Doppler INTERVENTIONS flow. Examples of ganglia that cause entrapment neu- US-guided needle placement to the perineural ropathies are shown in Figure 1. When aspirating a region requires coordination of transducer position ganglion, a large-gauge needle (such as an 18- or and needle location to deliver medication to the 16-gauge) is necessary as the contents of the ganglia appropriate location. Difficulty visualizing the needle will usually have a very viscous or jellylike consistency. before advancement and unintentional transducer Corticosteroids can be injected after the ganglion is movement make these procedures challenging for the decompressed, although the utility of corticosteroids novice operator.20 A variety of tools are available to for this indication has not been proven. assist with needle tracking such, as needle guides, Phenol and alcohol blocks have been used for lasers, and robotics (reviewed elsewhere).21 Both decades to treat spasticity related to upper motor neuron authors find it easier to have the same operator hold- . For refractory painful entrapment mononeuro- ing the probe as well as the needle, although others pathies in that only supply cutaneous sensation, find it easier to have 2 individuals performing the pro- such as the lateral cutaneous nerve of the thigh (lateral cedure. Real-time needle tracking can be divided into femoral cutaneous nerve), chemical neurolysis with “in-plane” and “out-of-plane” techniques (Fig. 2), both these agents can be an alternative to the more traditional of which have their strengths and weaknesses. Advan- surgical neurolysis. The downside, when compared with tages of the in-plane approach include the ability to corticosteroid injections, is that neurolysis will result in a see the needle shaft and tip during the entire proce- sensory deficit in the areas innervated by the nerve. dure and the ability to access both the superficial and There is also a theoretical risk of residual paresthesia deep aspects of nerves for hydrodissection. Advantages based on reports from the spasticity literature.16 of the out-of-plane approach include a more direct Recently, US-guided minimally invasive procedures access of some superficial structures and a less-steep have been developed for entrapment neuropathies. learning curve. The major disadvantage of the out-of-

FIGURE 1. Examples of cysts that can be treated by US-guided drainage. (A) An example of a patient with a suprascapular neuropathy secondary to a spinoglenoid ganglion, which is bordered by the infraspinatus (IS) anteriorly, the scapula (S) posteriorly, and the humerus (H) laterally. (B) After drainage, the ganglion (asterisk) is barely visible. (C) A longitudinal view of an intraneural ganglion of the fibular nerve. Arrows point to the nerve on either side of the ganglion.

AANEM Monograph MUSCLE & NERVE September 2019 223 FIGURE 2. Needle orientation with respect to the transducer. (A) An in-plane approach demonstrates the entire length of the needle with a bevel and a comet tail artifact underneath (arrows). (B) An out-of-plane approach will display the needle as a hyperechoic dot on the screen (arrowhead). [Color figure can be viewed at wileyonlinelibrary.com] plane approach is that the location of the needle tip compendium of easy-to-make and low-cost phantoms cannot always be determined on the screen (Fig. 3), using common items in the community and health-care and it is not possible to access the inferior boundary of facilities may be helpful for the interested reader the nerve utilizing this approach. (https://www.ultrasoundtraining.com.au/foamus/diy- In-plane needle guidance comes with a steep learning phantom-compendium). When performing in-plane curve before competency is achieved.22 Practicing on US-guided interventions, positioning the patient and cadavers or phantoms (commercial or homemade the operator in “a line-of-sight approach,” where objects that replicate human tissues) may be helpful the operator’s eyes are lined up with the shaft of the before performing the procedures on live patients. Low- needle, the short axis of the US probe, and the US cost nerve block models have been developed,23 and a machine (Fig. 4), can decrease procedure time and

FIGURE 3. The major drawback of the out-of-plane approach is that, although (A)–(C) illustrate very different locations of the needle tip, all appear as a hyperechoic dot (D) on the US screen. [Color figure can be viewed at wileyonlinelibrary.com]

224 AANEM Monograph MUSCLE & NERVE September 2019 help avoid musculoskeletal injuries that can affect up to 80% of US operators.27

PERFORMING THE PROCEDURES AND POTENTIAL COMPLICATIONS Careful preprocedure planning is the most important step in successfully performing an US-guided interven- tion. Because these procedures can be both technically challenging and painful for patients, a stepwise approach can be helpful. Table 1 outlines one such stepwise approach, which can be remembered by the mnemonic “ ”27 FIGURE 4. The line-of-sight approach. This setup can decrease APPLES. Surface anesthesia can be accomplished procedure time and improve accuracy, especially among novice with topical or vapocoolant spray. The authors operators. It is similar to the way that many play pool when they prefer the latter and will pass the needle through the line up the shaft of their stick with the ball and the hole. [Color fig- stream of spray directly. Vapocoolant spray has been ure can be viewed at wileyonlinelibrary.com] shown to be bactericidal and may increase procedure sterility.28 However, if spray is used adjacent to the probe, increase accuracy.24 If the needle is not visualized after a probe cover will prevent any damage. For many super- entry, simple sweeping (Fig. 5A) of the probe while ficial nerves, either a 25- or 27-gauge 1.5-inch needle will maintaining it parallel to the stationary needle will suffice. Advantages of the 25-gauge include widespread often bring the needle into view. Other strategies to availability in clinics, easier visualization of the needle, cope with the phenomenon of the “disappearing nee- and less risk of clogging the needle with corticosteroid, dle” include utilizing Doppler flow, beam steering,25,26 whereas the 27-gauge is often less painful for patients. utilizing a small-amplitude jiggling of the needle to see For peripheral nerves deeper than 2 cm, a longer nee- reverberation in the tissues, and performing a “heel– dle, such as a 21-gauge 2-inch needle, spinal needle, or toe” or “rocking” maneuver with the probe (Fig. 5B) to echogenic needle, may be necessary. The latter are spe- improve visualization of the needle by bringing the cially designed to allow for easy visualization under US.29 sound waves perpendicular to the long axis of the nee- Beam steering can also improve needle visualization for dle. Proper ergonomic positioning is important and deeper targets,25,26 but is generally not needed for more keeping the screen and patient within the same line of superficial nerves. The authors have found that when sight and limiting operator shoulder abduction can performing a procedure with a larger gauge needle,

FIGURE 5. Probe movements commonly utilized during US-guided procedures. (A) Sliding or sweeping: the probe is translated to the right or the left. Once the needle is inserted, often this is the only movement needed to visualize the needle. (B) Heel–toe maneuver or rocking: one part of the probe is pressed down into the tissue. This can be helpful in cases where there is a steep angle of entry (such as injections of the ), as it can reduce anisotropy and make the needle easier to visualize. [Color figure can be viewed at wileyonlinelibrary.com]

AANEM Monograph MUSCLE & NERVE September 2019 225 The major complications of US-guided treatment Table 1. Steps to consider when starting out performing peripheral nerve ultrasound-guided intervention. of peripheral entrapment mononeuropathies include infection, bruising and bleeding, postprocedure pain, Approach Perform a screening scan, avoid blood vessels, and choose the safest approach with respect to angle of and inadvertent nerve damage. Infections are gener- entry and distance from the transducer with the least ally less common in peripheral nerve interventions amount of tissue between the needle entry point and the than they are for joint injections. In the next target. Consider marking the location of the transducer and the location of needle entry with a skin pen. section we cover the approach to common entrap- Position Position the patient to optimize approach. Transducer ment neuropathies. Table 2 details strategies for suc- cover and preparation is completed at this point. cessful US-guided procedures, and Figure 6 shows Perpendicular Make sure probe is perpendicular to the skin so that the sound beam hits the needle directly. images of the procedures for individual entrapment Lift Lift up the edge of the transducer closest to the needle mononeuropathies, also assessed in what follows. to verify orientation of the transducer relative to the needle. Enter Needle entry is performed with the needle lined up APPROACH TO ULTRASOUND-GUIDED TREATMENT OF exactly with the long axis of the probe. INDIVIDUAL ENTRAPMENT MONONEUROPATHIES Sweep If the needle not visualized after entry, sweep (Fig. 5A) the Median Neuropathy at the Wrist (Carpal Tunnel probe left and right parallel to the needle until it is Syndrome). Anatomy and Symptoms. The median visualized while keeping the needle in the same position. nerve travels through the carpal tunnel where it sup- plies muscles of the thenar eminence as well as the first 2 lumbricals and provides sensory innervation to the anesthetizing a track from the skin to the nerve with a palmar aspect and finger tips of the thumb and index skin wheel utilizing a 25- or 27-gauge needle provides and middle fingers and half of the ring finger. Patients greater patient comfort. Once visualized, it is valuable to with CTS can present with wrist pain, numbness in save and archive an image of the needle and the target digits 1–3, weakness of thumb abduction, and noctur- structure. nal acroparesthesias. A palmar cutaneous branch of

Table 2. Helpful tips for obtaining optimal views for ultrasound-guided interventions and successfully performing the procedures.

Neuropathy Localization Pearls Pitfalls

Median neuropathy at the wrist To visualize the nerve in the short Either a radial (lateral) or an ulnar The flexor carpi radialis and (carpal tunnel syndrome) axis, place the transducer over (medial) approach can be used median nerve can have a similar the wrist crease. The nerve will when injecting using a appearance. The relatively appear as a relatively transverse approach. increased anisotropy of the hypoechoic (dark) structure. tendon can help distinguish the 2 nerves. Ulnar neuropathy at the elbow Place the transducer spanning the Injecting just proximal to the medial It can be challenging to access the (cubital tunnel syndrome) medial epicondyle and the epicondyle is technically easier in some individuals olecranon and a transverse view and may result in spread of at the level of the medial of the ulnar nerve should be injectate to all potential epicondyle and olecranon easily obtained. entrapment sites with a single secondary to obstruction from injection. the bones. Deep branch of the Place the transducer over the may mimic The nerve will sometimes increase neuropathy (radial tunnel dorsum of the upper lateral epicondylitis clinically. in cross-sectional area at the syndrome) and look for the nerve between arcade of Frohse, even in normal the 2 heads of the supinator. individuals. Suprascapular neuropathy The nerve can be visualized at the Visualization of the nerve at the It can often be challenging to cortical line on the top of the spinoglenoid notch can visualize the nerve, especially at suprascapular fossa or in the sometimes be facilitated by the spinoglenoid notch. region of the spinoglenoid notch identifying the suprascapular when the infraspinatus is viewed artery with Doppler flow. in the longitudinal axis. Lateral cutaneous nerve of the The nerve can usually be identified Electrical stimulation during the The site of entrapment at the thigh neuropathy (meralgia in a fat plane between the procedure can sometimes help inguinal ligament can be paresthetica) sartorius and tensor fasciae confirm needle placement near challenging to visualize. latae muscles. the nerve, especially in larger individuals. Sciatic neuropathy (piriformis Locate the posterior superior iliac The piriformis muscle location can The has a variable syndrome) spine and move the probe be confirmed by external course through the piriformis inferiorly while rotating the lateral rotation of the hip to demonstrate and can sometimes be very hard aspect of the probe caudally. muscle movement relative to the to visualize in obese individuals. . Fibular (peroneal) nerve at the The nerve can be visualized The nerve can appear normal in a The exact site of entrapment may fibular neck neuropathy superficially as it courses around fibular entrapment be difficult to visualize as the the fibular neck and traced mononeuropathy. nerve takes an acute turn at the proximally to the junction with fibular neck. the .

226 AANEM Monograph MUSCLE & NERVE September 2019 FIGURE 6. Examples of US-guided perineural injection of the median nerve (A), ulnar nerve (B), deep branch of the radial nerve (C), lat- eral cutaneous nerve of the thigh (D), and sciatic nerve at the level of the piriformis (E). Examples of US-guided drainage of a spin- oglenoid ganglion (F) and an intraneural ganglion of the fibular nerve (G) in the transverse plane. The same ganglion is displayed in the longitudinal plane in Figure 1C and yielded 40 ml of fluid on aspiration. Nerves are denoted by asterisk and needles are denoted by arrows. TFL, tensor fasciae latae. [Color figure can be viewed at wileyonlinelibrary.com] the median nerve arises just proximal to the carpal tun- also can identify anatomic abnormalities such as a bifid – nel to innervate the skin overlying the thenar emi- median nerve and persistent median artery.31 33 Corti- nence itself. The carpal tunnel is bounded dorsally by costeroid injections are an established treatment to alle- the transverse carpal ligament, which can be visualized viate the pain and numbness associated with CTS. The on US, and ventrally by the carpal bones. It contains authors typically reserve injections for patients with the flexor tendons to all fingers, which can easily be mild-to-moderate median neuropathy at the wrist. distinguished from the median nerve in the transverse When a patient presents to the EDx laboratory with plane by toggling the probe to demonstrate the rela- moderate-to-severe axon loss of motor fibers, surgical tively increased anisotropy of the tendons relative to management may be preferable to injection therapy the nerves. The tendons of the flexor carpi radialis given the risk of worse surgical outcome with more pro- (FCR) are not contained in the carpal tunnel but gressive nerve damage. Corticosteroid injections are course alongside the median nerve at the wrist crease also useful for postsurgical CTS as they may relieve the and can easily be mistaken for the median nerve. Like adhesions that form from the scar tissue34 and may pre- the flexor tendons to the fingers, the FCR can be dis- dict response to a second surgical release.35 tinguished from the median nerve by its increased In addition, ganglion cysts can exert a mass effect anisotropy. In addition, the median nerve will dive resulting in CTS. These tend to arise from the deeper proximal and distal to the wrist crease, whereas scapholunate joint and are more common in women. the FCR will stay relatively superficial. Aspiration of these cysts can be helpful in relieving symptoms, although ganglion cysts treated by aspira- Ultrasound-Guided Interventions. EDx studies and tion have an approximately 59% risk of recurrence.36 US both can support the clinical diagnosis of CTS. US Although corticosteroid injections are a mainstay of can sometimes increase diagnostic yield in patients with conservative CTS treatment, they have been found to be clinically evident CTS but negative EDx studies,30 and inferior to surgery in the long term.37 Multiple recent

AANEM Monograph MUSCLE & NERVE September 2019 227 studies, including a meta-analysis, have demonstrated Deep Branch of the Radial Nerve Neuropathy (Radial that injections performed with US guidance can be Tunnel Syndrome). Anatomy and Symptoms. The – more efficacious than those without.38 42 In-plane trans- radial nerve splits into the superficial and deep bra- verse median nerve injections can be performed from nches after passing anterior to the lateral epicondyle. either a radial (lateral) or an ulnar (medial) approach.43 The deep motor branch of the radial nerve then passes The advantage of the ulnar approach is that it avoids through the arcade of Frohse and emerges as the pos- most tendons and the palmar cutaneous nerve, whereas terior interosseous nerve (PIN), which supplies the the radial approach has the advantage of avoiding the extensors of the wrist and fingers distal to the extensor ulnar artery. Sometimes, individual patient anatomy will carpi radialis longus. Although it does not have any determine the approach. Studies have demonstrated cutaneous fibers, it does supply sensory innervation to reduced nerve mobility in CTS,44,45 and histopathology the wrist joint itself; therefore, patients with radial tun- has demonstrated increased activity of fibroblasts in the nel syndrome may complain of pain either at the subsynovium, which results in adhesions.34 Mechanical arcade of Frohse (the site of entrapment) or at the hydrodissection may relieve these adhesions46 and is far wrist, but cutaneous sensation should be normal on easier to perform using an in-plane transverse approach. physical examination. In addition to the injection, operators can repeatedly fenestrate or “release” the transverse carpal ligament Ultrasound-Guided Interventions. In cases where it ’ with a needle,17,47 or perform a minimally invasive is not clear whether a patient s weakness is due to release with a specialized surgical instrument.18,19,48 common extensor tendinosis () or entrapment at the arcade of Frohse, diagnostic injec- tions can aid surgical planning. Unlike CTS and Ulnar Neuropathy at the Elbow (Cubital Tunnel cubital tunnel syndrome, it may be very challenging Syndrome). Anatomy and Symptoms. The ulnar to diagnose neuropraxic lesions of the deep branch nerve descends from the medial cord of the brachial of the radial nerve on EDx grounds given the chal- plexus. Just proximal to the elbow it courses through lenges in obtaining an accurate conduction velocity the arcade of Struthers, then past the medial epi- across the site of the lesion. condyle under the arcuate ligament, and then finally There is only 1 case report of a patient with the PIN to the cubital tunnel, which is formed by the 2 heads of being treated with an US-guided intervention.54 An in- the flexor carpi ulnaris. The nerve supplies innervation plane, transverse approach will allow injection of the to the ulnar innervated finger flexors and the intrinsic perineural region with or without hydrodissection from hand muscles not innervated by the median nerve. the surrounding supinator muscle, but evidence to Patients with cubital tunnel syndrome typically have support the efficacy of this procedure is lacking. weakness in finger abduction as well as sensory changes in the fourth and fifth digit along with normal cutane- ous sensation proximal to the wrist crease. Suprascapular Neuropathy. Anatomy and Symp- toms. The suprascapular nerve originates from the Ultrasound-Guided Interventions. Theroleofcorti- upper trunk of the and courses costeroid injections in ulnar neuropathy at the elbow through entrapment sites at the suprascapular notch (UNE) is not currently clear. Although several case series and spinoglenoid notch. It sends off sensory fibers to have shown that US-guided corticosteroid injections can the shoulder joint, but, like the deep branch of the 49–51 improve symptoms, a randomized, controlled trial radial nerve, it does not supply cutaneous innerva- did not demonstrate any benefit of a corticosteroid injec- tion and lesions can be challenging to diagnose with 52 tion when compared with placebo injection. In the nerve conduction studies (NCSs) and needle electro- authors’ experience, ulnar nerves with larger cross- myography (EMG) when they are neuropraxic. sectional area (CSA) are more likely to respond to a cor- Patients with suprascapular neuropathy typically have ticosteroid injection than ulnar nerves with lower CSA. shoulder pain, weakness of shoulder external rota- Perineural injection of the ulnar nerve can be per- tion, and a normal sensory exam. formed anywhere along the potential entrapment sites. An in-plane transverse approach between the medial Ultrasound-Guided Interventions. Entrapment of epicondyle and olecranon has been shown to result in the nerve at the spinoglenoid notch or suprascapular good spread of the injectate to all sites of potential notch may be found in the context of a ganglion – entrapment in a recent cadaver study.53 Careful cyst.55 59 Drainage of these cysts with a large-gauge patient positioning when using an in-plane transverse needle has been reported to provide relief of symp- approach is often necessary given that access to the toms.56,58,60 The efficacy of US-guided interventions nerve can be blocked by the medial epicondyle or the for treatment of suprascapular neuropathies second- olecranon. There is currently no evidence to support a ary to other etiologies has not yet been established, role for needle release of the cubital tunnel, arcuate but diagnostic blocks may be helpful in confirming a ligament, or arcade of Struthers. suspected diagnosis.

228 AANEM Monograph MUSCLE & NERVE September 2019 Lateral Cutaneous Nerve of the Thigh Neuropathy (Meralgia neurotoxin injections into the piriformis muscle have Paresthetica). Anatomy and Symptoms. The lateral been shown to have a positive effect in several case – cutaneous nerve of the thigh (LCNT) is formed from series.76 79 the L2 and L3 nerve roots and contains only cutane- ous fibers. It courses from the lumbar plexus medial Fibular (Peroneal) Nerve at the Fibular Neck to the anterior superior iliac spine and then supplies Neuropathy. Anatomy and Symptoms. The fibular sensory innervation to the lateral thigh and demon- (peroneal) nerve splits from the tibial nerve in the pop- 61 strates a fair amount of anatomic variability. The syn- liteal fossa and courses around the fibular neck where drome of meralgia paresthetica can occur when the it may become entrapped before supplying cutaneous nerve is compressed under the inguinal ligament due innervation to the lateral shin and foot and motor to mechanical abnormalities related to large body hab- innervation to the dorsiflexors and everters of the fi 62 itus or tight- tting clothing. It presents with pares- ankle. Patients with fibular entrapment mononeuro- thesia, pain, or numbness in the lateral aspect of the pathies often present with foot drop and variable fl thigh with preserved motor strength and re exes. degrees of sensory loss. Like UNE, neuropraxic fibular neuropathies can be easily diagnosed with NCSs by Ultrasound-Guided Interventions. Sensory nerve measuring a conduction velocity across the affected seg- action potentials can be challenging to elicit even in nor- ment. About 18% of EDx-confirmed idiopathic fibular mal individuals, and therefore injections of the LCNT neuropathies are associated with a cyst arising from the – can be helpful for diagnostic purposes. Several case proximal tibiofibular joint.80 82 Otherwise, neuromus- series have demonstrated that corticosteroid injections fi fi 63–66 cular US images of patients with EDx-con rmed bular can relieve the symptoms of meralgia paresthetica. neuropathies are often normal. Surgical management includes surgical neurolysis. It is also possible that chemoneurolysis with alcohol or phe- Ultrasound-Guided Interventions. Perineural injec- 67,68 nol could help in refractory cases, but this calls for tion of the fibular nerve is not known to be an effective further research. treatment. US-guided drainage of the perineural space (Fig. 6G) and corticosteroid injection of an intraneural 83 Sciatic Neuropathy (). Anatomy ganglia has been reported in 1 case report. and Symptoms. ThesciaticnervearisesfromtheL4–S2 nerve roots and courses out of the sciatic notch toward CONCLUSION AND FUTURE DIRECTIONS the piriformis muscle. Although it most commonly US-guided treatment of peripheral entrapment travels inferior to the piriformis muscle, sometimes it mononeuropathies is rapidly expanding in clinical can pierce the piriformis muscle or even travel superi- practice alongside the expansion of neuromuscular orly to the piriformis. Piriformis syndrome is a some- US. A detailed knowledge of sonoanatomy, careful pro- what controversial entity69 characterized by sensory and cedure planning, and close coordination of transducer sometimes motor changes in the distribution of the sci- and needle movement are essential to a successful atic nerve with pain in the gluteal region, especially with US-guided intervention. Evidence is mounting that US- sitting. guided treatment of CTS is superior to nonguided interventions. Although corticosteroid injections and Ultrasound-Guided Interventions. It is often unclear aspiration of ganglia are the most commonly per- whether the pain generator is the piriformis muscle, formed procedures in this field, emerging minimally the sciatic nerve, or a combination. As with other invasive procedures are becoming more common and entrapment mononeuropathies described previously, offer the possibility of symptomatic resolution compa- mild piriformis syndrome can often be silent on EDx rable to a surgical release but with the recovery time of testing in mild cases. US-guided injections of the an injection procedure. Although high-quality evi- piriformis muscle in the region of the sciatic nerve can dence is not yet available for many other entrapment provide confirmation of the diagnosis in many cases, as neuropathies, US-guided treatment may be a helpful well as provide therapeutic relief. diagnostic and therapeutic tool. Further research is Injections for piriformis syndrome can be performed needed to determine the efficacy of corticosteroid using an in-plane transverse approach with corticoste- injections, define the doses and approaches that are roid, and US has been shown to be comparable to fluo- most efficacious, as well as elicit the possible benefits of – roscopy in terms of accuracy.70 72 One case series hydrodissection. There is also a need for more studies demonstrated that US-guided injections can be helpful,73 comparing US-guided minimally invasive procedures but a recent report suggested that corticosteroid may not with both routine US-guided injections and surgical offer any additional benefit over local anesthetic alone.74 releases. In summary, neuromuscular specialists can Another recent report described the pairing of hydrodis- best advise patients on potential treatments when they section of the sciatic nerve with corticosteroid injection75 obtain an understanding of US-guided treatment of as a treatment for piriformis syndrome. In addition, entrapment mononeuropathies. Integration of both

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